1. Field of the Invention
The present invention relates to an inkjet printer having a filter for removing foreign materials from ink, wherein the filter is disposed in an ink path for supplying ink to the inkjet head. More particularly, the present invention relates to an inkjet printer capable of avoiding print defects and other problems resulting from air bubbles trapped at the ink filter.
2. Description of Related Art
When foreign materials is present in the ink supplied from the ink tank to the inkjet head of an inkjet printer, the ink nozzles of the inkjet head can become clogged, leading to ink discharge problems and printing defects. A filter for removing such foreign materials is, therefore, commonly disposed in the ink supply path near the inkjet head to prevent the foreign materials from penetrating the inkjet head together with the ink.
Removable ink cartridges are now often used as the ink tank. Removing an empty ink cartridge to replace it exposes the ink supply path to the air, which can then enter the ink supply path and become trapped therein, forming a bubble. After the ink cartridge is replaced, and the ink charging operation is performed to supply ink from the ink cartridge to the inkjet head, the air bubble inside the ink supply path is also pushed toward the inkjet head.
No problems occur if the bubble is then expelled through the ink nozzles to the outside of the inkjet head. However, the bubble sometimes becomes trapped by the filter and, thus, remains inside the ink supply path. When a bubble becomes trapped by the filter, it becomes a nucleus around which other bubbles congregate, and the bubble gradually grows. This can lead to the following problems.
One problem is that, the trapped air bubble makes ink supply unstable. As a result, when the required volume of ink is not supplied to the ink nozzle, ink drop discharge defects occur. Furthermore, when the trapped bubble grows to a sufficient size, it can completely block ink drop discharge.
The present invention has been developed in light of the above noted problems. It is, therefore, an object of the present invention to provide an inkjet printer that can automatically eliminate bubbles trapped in the filter.
To achieve this and other objects, an inkjet printer according to the present invention includes: an inkjet head; an ink-intake opening formed in the inkjet head; a filter for removing foreign materials contained in ink supplied to the ink-intake opening, the filter being disposed in an ink path on an upstream side of the ink-intake opening; and a connection block disposed above the filter and having an ink path to the filter. The connection block has an ink-supply-line part wherein an ink-path portion is formed with a substantially constant shape in cross section, and an ink-path-connection part forms another ink-path portion extending from the bottom of the ink-supply-line part to the filter. The internal volume of the ink-path-connection part is equal to or less than the volume of a sphere internally tangent to the ink-supply-line part.
When a bubble trapped in the ink-path-connection part separates from the filter top, and becomes a spherical bubble, the bubble will not be larger than one which can pass through the ink-supply-line part. Therefore, the buoyancy of the ink acting on the trapped bubble automatically causes the bubble to rise through and pass out from the ink-supply-line part.
In one embodiment of the present invention, the ink-path-connection part of the connection block has a substantially conical shape. The resulting tapered shape thus permits the bubbles on the filter top to rise reliably along the tapered surface and pass out from the ink path.
In another embodiment of the present invention, the inside wall surface forming the ink-path-connection part is an inwardly bulging curved surface.
In yet another embodiment of the present invention, the ink-supply-line part and ink-path-connection part of the connection block are disposed substantially vertically. This arrangement assures that there is nothing on the inside surface of the ink-supply-line part and ink-path-connection part obstructing the rise of the bubble. Thus, bubbles are reliably expelled.
In another embodiment of the present invention, the sectional shape of the ink-path-connection part is substantially cylindrical. As a result, the shape of a spherical bubble rising due to buoyancy will not be disturbed and, thus, the bubble can pass smoothly up and out from the ink-supply-line part.
In yet another embodiment of the present invention, the filter is disposed at the ink-intake opening, near the inkjet head. Disposing the filter near the inkjet head assures that bubbles reliably can be prevented from entering the inkjet head.
In still yet another embodiment of the present invention, a bubble trapxe2x80x94for holding a bubble rising through the ink-supply-line partxe2x80x94is disposed above the connection block on an upstream side of the ink path. Bubbles, trapped at the filter, which then rise by buoyancy up through the connection block, can be captured and held in the bubble trap. As a result, once bubbles are removed from the filter surface, they can be prevented from flowing back through the ink-supply-line part to the filter wherein they would again become trapped at the filter surface.